The invention relates to a telecommunications system for transmitting images according to the preamble of patent claim 1.
In communication systems having a message transmission link between a message source and a message receiver, transmitting and receiving devices are used for message processing and transmission. The message produced by the message source is transmitted from the transmitting device via a communication channel to the receiving device, which subsequently delivers the received message to the message receiver. The message processing and transmission may in this case take place in a preferred direction of transmission or in both directions of transmission (duplex operation).
"Message" is a generic term which stands both for the meaningful content (information) and for the physical representation (signal). In spite of the same meaningful content of a message--that is to say the same information--different signal forms may occur. For example, a message concerning one subject may be transmitted
(1) in the form of an image, PA0 (2) as a spoken word, PA0 (3) as a written word, PA0 (4) as an encoded word or image.
The type of transmission according to (1) . . . (3) is in this case normally characterized by continuous (analog) signals, while in the case of the type of transmission according to (4) usually discontinuous signals (for example pulses, digital signals) are produced. The present invention relates primarily to the transmission of visual messages (for example images, personal recordings (videos), diagrams, lettering etc) and, to complement this, it relates to a combination of the transmission of visual messages and acoustic messages (for example image/sound transmission etc), the respective signal form generally being a mixture of continuous signals and discontinuous signals. Depending on this message type, on which the invention is based, for the communication system (telecommunications system) defined above there are required in each case message-type-specific telecommunication devices for the functions of "transmitting" and "receiving". The question as to which telecommunications devices are ultimately used depends, inter alia, also on which communication channel is taken as a basis in the communication system. For the present invention, the communication channel is of only secondary significance, because the principle of the invention can be applied to wired and/or wireless telecommunications channels.
With respect to the already mentioned directions of transmission within the communication system, for the present invention unidirectional message transmission is the primary form. However, this in turn does not mean that it cannot also be used for duplex operation.
In the transmission of images according to the above definition, a distinction is made between moving image transmission and individual image transmission. The most widespread application of image transmission is television engineering, in which both individual images and moving images are transmitted via wired and wireless communication channels. On this basis, there were initial attempts in the 70s to develop video telephones which transmit images over the existing telephone network from a transmitter (A subscriber) to a receiver (B subscriber). The first video telephones primarily comprised three individual device elements, namely a telephone, a camera and a monitor. The innovative development of microelectronics and communication transmission technology means that today there are already integrated video telephones, in which these device elements are combined in a single telephone. The development of such video telephones, working in duplex operation, has come very much to the forefront in recent years from the aspect of moving image transmission in accordance with CCITT Standard H.261 for video communication. Published patent applications which document this development trend are, for example, EP-A1-0 506 544, EP-A2-0 523 618, EP-A2-0 524 623 and EP-A2-0 523 617. However, apart from the fact that the image transmission is quite slow, expensive and not mobile, the realization of such moving image telephones has the disadvantage that the application is limited by standard incompatibility, because the telephone device and video device are inseparably connected in one device and therefore video telecommunication can take place only among those communication subscribers which have the same video telephone. This can in particular have the result--in the case of such fixed forms of transmission--that there are restrictions for the transmission systems, such as the ISDN system.